This invention relates to controlling a rotating knife to cut a continuous, moving sheet of material into predetermined lengths.
Several difficulties are encountered when rotary knives are used for cutting a continuous moving sheet of material. If the circumference of the rotating knife cylinder is not identical to the predetermined length of material to be cut, the rotary knife cannot run continuously synchronously with the continuous moving sheet. Generally, the circumference of the rotary knife is less than the predetermined lengths into which material is cut which necessitates that the rotating knife speed be changed during each rotation. One method to allow for a sufficient length of material to pass the cut point before the knife completes its rotation and cuts another predetermined length of material requires that the knife be parked during a portion of each revolution. Once the knife is stopped in a park position, the complexity of controlling the knife is compounded because the knife rotation must be started at an appropriate time and the rotation controlled in such a manner as to synchronize the rotating knife with the moving line of material to cause the knife to cut a predetermined length of material. Many feedback control methods exist to determine when the knife rotation should commence from a park position and how the rotation of the knife should be controlled to properly cut a predetermined length of material. The control method should provide accurate starting, accelerating and positioning of the knife with respect to the moving material line to cut the material into predetermined lengths. Accurate yet simple control is of even greater concern when the control method is implemented using a microprocessor and control in real time necessitates that the calculation be accurate yet not complex, thereby permitting real time control of the rotating knife. Many of the prior art control methods were too complex and therefore did not lend themselves to real time control implemented using a microprocessor.